Flux is a pattern that Facebook uses for
building front-end web applications.

It complements React's components with
a unidirectional data flow.

Flux

Flux

Motivation...

Flux

Flux

Flux

Flux

Flux is not a library

It is just a pattern

a guideline...

The race had begun

Alt

DeLorean.js

Flummox

McFly

marty.js

RefluxJS

Fluxible

material-flux

A list of OS Projects using Redux...

Critical Mass votes for Redux

The race was won

implementation

Single source of truth

all application state is stored as
a single  JS object

store

1st Principle 

The state tree is immutable 
(Read-only)

You cannot write to or modify the app state directly

store

2nd Principle 

To modify application state You need to dispach an   Action

Actions are payloads of information
They are the only source of data of the store.

const ADD_TODO = 'ADD_TODO'

{
  type: ADD_TODO,
  text: 'Build my first Redux app'
}

Action Creators are functions
that create and return actions

const ADD_TODO = 'ADD_TODO'

function addTodo(text) {
  return {
    type: ADD_TODO,
    text: text
  }
}

3rd Principle                            Changes are made with pure functions

A reducer is a pure function that takes the previous state and an action, and returns the next state.

( previousState ,  action ) =>  newState

 Reducers   Handle Actions

Handling Actions in Reducers

function todoApp(state = initialState, action) {

  switch (action.type) {

    case SET_VISIBILITY_FILTER:
      return {
        ...state,
        visibilityFilter: action.filter
      }

    case ADD_TODO:
      return {
        ...state, 
        todos: [...state.todos,
                { 
                  text: action.text,
                  completed: false
                }]
      }
   
    default:
      return state
  }
}

Combine Reducers

reducers/index.js


import { combineReducers } from 'redux'
import todos from './todos'
import counter from './counter'

const  rootReducer = combineReducers({
  todos,
  counter
})

export default rootReducer

To create the    store   instance
use the redux method createStore()

createStore() requires a root reducer as 1st param
and optionally - an initialState and an enhancer  

import { createStore, applyMiddleware } from 'redux'

import   rootReducer   from './reducers'

let store = createStore(rootReducer , 
                        {count:8} , 
                        applyMiddleware(...))

applyMiddleware(...middleware)

Middleware are functions used to extend Redux
They are composable by design
Each function requires no knowledge of what comes before or after it in the chain.

Home made Middleware

Middleware functions have the following signature:

import { createStore, applyMiddleware } from 'redux'

import   rootReducer   from './reducers'



const logger = store => next => action => {
    console.log('dispatching', action)
    next(action)
    console.log('next state', store.getState()
}

let store = createStore(rootReducer , 
                        {count:8} , 
                        applyMiddleware(logger) )

Home made Middleware

const logger = store => next => action => {
  console.log('dispatching', action)
  next(action)
  console.log('next state', store.getState())
}

function logger(store) {
  return function(next) {
    return function(action) {
      console.log('dispatching', action)
      next(action)
      console.log('next state', store.getState())
    }
  }
}

Same as writing:

3rd party Middleware

Same function signature as home-made middleware
serve as Redux 'plugins' and available as npm packages

import { createStore, applyMiddleware } from 'redux'

import   thunk   from 'redux-thunk'

import   rootReducer   from './reducers'

import   logger   from './my-middleware/logger'

let store = createStore(rootReducer , 
                        {count:8} , 
                        applyMiddleware(thunk,logger) )

regular Action Creator functions
create and return action objects

const ADD_TODO = 'ADD_TODO'

function addTodo(text) {
  return {
    type: ADD_TODO,
    payload: text
  }
}

dispatching async actions with
redux-thunk middleware

Async action creators return a callback with a promise
The callback will receive the store dispatch method as a parameter
* The following code will work only if redux-thunk middleware was used at the store creation

function fetchPosts(topic) {

   return async (dispatch)=> {
        try{
             dispatch(fetch_posts_start(topic))   // START     

             const url = `https://myblog.com/api/${topic}`

             const response = await fetch(url)
             const data = await response.json()
             dispatch(fetch_posts_success(topic, data)) // SUCCESS 

        }catch(error){

             dispatch(fetch_posts_failed(error)) // FAILED 
        }

   }
}

applyMiddleware(...middleware)

Middleware are functions used to extend Redux
They are composable by design
Each function requires no knowledge of what comes before or after it in the chain.

tightly coupled with React

You can write Redux apps with React, Angular, Ember, jQuery, or vanilla JavaScript.

is not 

Official React bindings for Redux

<Provider store> 

Connect(...)

<Provider store> 

Wraps the root component,
Providing access to the Redux store

ReactDOM.render(
  <Provider store={store}>
    <MyRootComponent />
  </Provider>,

  document.getElementById('root')
)

Connect(...)

• Connects a React component to a Redux store.
• Components connected to a Redux store
  are typically called Containers
• Whenever the store will update, so will the container

import { connect } from 'react-redux'

let ProfilePage = () => {
  return (
    <div>
      ...
    </div>
  )
}

export default connect(...)(ProfilePage)

update the view with
mapStateToProps( state )

To use connect(), define a mapStateToProps function

It maps the parts of the store state your container cares about
into props it will pass down to its child components

import { connect } from 'react-redux'

let ProfilePage = ({ active }) => {
  return <div>...</div>
}

const mapStateToProps = (state, ownProps) => {
  return {
    active: ownProps.filter === state.visibilityFilter
  }
}

export default connect(mapStateToProps)(ProfilePage)

import { someActionCreator,increment,decrement,toggleTodo} from './actions'

const mapDispatchToProps = (dispatch, ownProps) => {
  return {

     doSomething: ()=>     dispatch( someActionCreator() )

     doIncrement: ()=>     dispatch( increment() ),
     doDecrement: ()=>     dispatch( decrement() ),

     onTodoClick: (id)=>   dispatch( toggleTodo(id) )
  }
}

export default connect(mapStateToProps, mapDispatchToProps)(ProfilePage)

dispatching actions with
mapDispatchToProps( dispatch)

Optional  second parameter of connect(),
It recieves dispatch() as a param and returns callback props
your container will typically inject down to its child components

* if not implemented, containers will have dispatch() available via props